The present invention relates in general to computer systems, and, more particularly, to apparatuses for sharing memory among multiple processors.
Multiprocessor computer systems have been commercially available for the past 30 years. Typical systems have multiple processors connected, through a variety of connection fabrics, to a single, shared memory system. Likewise, all input and output (IO) devices are connected to the multiple processors through a single IO channel. The operating system for these typical SMP systems is a single Operating System that has been parallelized to run over the processor complex.
Several disadvantages, inherent in such a system structure have prevented the systems from effectively scaling past 5 to 8 processors and have greatly elongated product delivery schedules. Those disadvantages are: 1. All memory requests must go though the connection fabric whether the data being requested is shared by multiple processors or only used by one processor, creating a bottleneck in the memory connection fabric; 2. The Operating System must be parallelized; 3. The parallel Operating System creates a great deal of extra memory requests; 4. All IO requests must go through the IO channel creating a bottleneck.
In recent years, distributed memory computers, such as Massively Parallel Processors, Clusters, and networked systems have emerged as potential solutions for the disadvantages of SMPs. Common applications of such networks include distributed computing environments, client-server systems, and server clustering implementations. In a typical LAN, information to be passed from one computer to another computer via the network is first transferred from an application running on the transmitting computers processor to a device driver: an operating system level, software-based object. The device driver assembles the message to be transferred into packets conforming to the protocol to be used for data transmission (such as conventional TCP/IP or IPX/SPX protocols).
These packets are transferred by the device driver to a conventional network card, such as a 10 or 100 megabit-per-second Ethernet network card. The network card then transmits the data over the physical layer of the network, where a similar network card on the receiving computer captures it. This captured data is then transferred to a similar software-based device driver on the receiving computer. This device driver will typically reconstruct the message sent by the transmitting computer, by decoding and unpacking the individual protocol packets transferred over the physical layer. The reconstructed message is then made available to an application running on the receiving computer.
As can be seen from the foregoing description, one disadvantage of such typical LAN systems is the delays imposed, on both the transmitting and receiving ends, from the presence of software-based layers, such as operating systems network device and transmission protocol drivers.
The present invention overcomes the limitations of the prior art systems. The invention significantly reduces the bottlenecks in both the memory connection fabric and the IO channel and eliminates the requirement to parallelize the Operating System and maintain the standard load/store (read/write). The invention also eliminates the requirement to pass messages between processors hence significantly reducing the data transfer times.
The present invention is directed to an adapter for coupling a processor (single or multiple) system to a shared memory unit over a data link, wherein the processor system includes a data bus for access to a local memory and a expansion bus coupled to the data bus, and, the shared memory unit includes at least one bank of shared memory. The adapter comprises: a expansion bus interface coupling the adapter to the expansion bus of the processor system; an input/output port coupling the adapter to the shared memory unit via the data link; means coupled to the expansion bus interface for monitoring processor memory accesses on the data bus; means coupled to the data bus monitoring means for detecting when a monitored processor memory access is a processor memory access operation to a memory address value within a range of addresses corresponding to the shared memory; means coupled to the detecting means for translating the monitored processor memory access operation into a shared memory access request; means for outputting the shared memory access request to the input/output port and, in turn, to the shared memory unit; and means coupled to the expansion bus interface for placing a memory access completion acknowledgement indication on the standard expansion bus, whereby it is transparent to the processor system whether the memory access operation is addressed to the local memory or to the shared memory.
In a preferred embodiment of the invention, the memory access operation may comprise at least one of a memory read operation or a memory write operation.
It is also preferred that the expansion bus interface comprises at least one of the following: a peripheral component interface bus interface, an Advanced Graphics Port bus interface, conventional memory module bus interface, or an Industry Standard Architecture bus interface. It is also contemplated that the input/output port comprises at least one of a Scalable Coherent Interface, an IEEE 1394 interface, a SCSI bus interface, an Ethernet network interface or an optimized parallel or serial interface. In one preferred embodiment, the processor system comprises a conventional IBM-compatible personal computer.
In another preferred embodiment, the processor system accesses the data bus and, in turn, the shared memory unit, via memory accesses placed upon the data bus from an unmodified conventional operating system.
It is also preferred that the unmodified conventional operating system comprises a uniprocessor build of a Windows NT or similar operating system.
In still another preferred embodiment, a combined memory space comprises the local memory of the processor system and the shared memory of the shared memory unit contains at least one memory address corresponding to a register location.
The present invention also is directed to a shared memory unit for providing shared memory to a plurality of processor systems. In such an embodiment, the shared memory unit comprises a shared memory comprising a plurality of memory banks; a plurality of input/output ports, each input/output port being connectable to a processor system by a dedicated data link; means coupled to the input/output ports for receiving a shared memory access request from a requesting processor; means coupled to the receiving means for determining the memory bank corresponding to the memory access request; connecting means coupled to the receiving means, the determining means, and the memory banks, for providing a data path between the input/output port and the memory bank associated with the memory access request; a memory controller coupled to the connecting means and the receiving means, the memory controller performing memory accesses to the shared memory bank through the connecting means in accordance with the memory access request; and means coupled to the memory controller and the input/output ports for generating a shared memory access response for transmission back to the requesting processor system.
In this preferred embodiment, the connecting means comprises a crossbar switch, which may comprise a non-blocking crossbar switch.
In a preferred embodiment of the invention of the invention, further includes means for providing atomic memory operations between at least one of the processor systems and the shared memory.
In another preferred embodiment, the invention includes a memory bus transfer controller for controlling accesses to a local portion of distributed shared memory. The memory bus transfer controller comprises: a local processor memory bus interface coupling the memory bus transfer controller to a local processor and to a memory private to the local processor; a local shared memory bus interface coupling the memory bus transfer controller to the local portion of distributed shared memory; a shared memory interconnect bus coupling the memory bus transfer controller to at least one remote memory bus transfer controller associated with at least one remote processor; first monitoring means coupled to the local processor memory bus interface for monitoring local processor memory bus accesses; first determining means coupled to the first monitoring means for determining whether a memory address associated with the processor memory bus access corresponds to one of the memory private to the local processor, the local portion of distributed shared memory, and a remote portion of distributed shared memory; second monitoring means coupled to the shared memory interconnect bus for monitoring remote processor memory access requests; second determining means coupled to the second monitoring means for determining when a remote processor memory access request corresponds to the local portion of distributed shared memory; and a memory controller coupled to the first determining means the second determining means, the local processor memory bus, and the shared memory interconnect bus. The memory controller performs a local shared memory access when the first determining means indicates that a local processor memory bus access corresponds to the local portion of distributed shared memory. This sends a shared memory access request to the shared memory interconnect bus when the first determining means indicates that a local processor memory bus access corresponds to a remote portion of distributed shared memory, and performs a local shared memory bus access when the second determining means indicates that a remote memory access request corresponds to the local portion of distributed shared memory; whereby it is transparent to the local processor whether each of its memory access operations is addressed to the local memory, the local portion of distributed shared memory, or a remote portion of distributed shared memory.
The invention is also directed to a method for performing processor memory accesses to a shared memory unit using an adapter coupling a processor system to the shared memory unit via a data link. The processor system includes a standard expansion bus. The adapter has a standard expansion bus interface coupling the adapter to the standard expansion bus of the processor system and an input/output port coupling the adapter to the data link and, in turn, to the shared memory unit. The method comprises the steps of: A) monitoring processor memory accesses on the standard expansion bus; B) detecting when a monitored processor memory access is a processor memory operation to a memory address value within a range of addresses corresponding to the shared memory; C) translating the processor memory operation into a shared memory access request; D) outputting the shared memory access request to the input/output port and, in turn, to the shared memory unit via the data link; and E) placing a shared memory access acknowledgement indication on the standard expansion bus; whereby it is transparent to the processor whether the memory access operation is addressed to the local memory or to the shared memory.